Current sensors using magnetostrictive material

Abstract

A current sensor device. The current sensor device includes a strain distribution converter; an optical fiber coupled with the strain distribution converter; and a magnetostrictive material associated with the strain distribution converter such that a change in shape of the magnetostrictive material causes a change in length of the optical fiber.

What is claimed is: 
     
       1. A current sensor device, comprising:
 a strain distribution converter; 
 an optical fiber having a plurality of modulations in refractive index, the plurality of modulations in refractive index being periodic modulations in an initial state without external excitation, and wherein a segment of the optical fiber is coupled with the strain distribution converter; and 
 an externally excitable magnetostrictive material associated with the strain distribution converter such that a change in shape of the magnetostrictive material under external excitation causes a change in length of the optical fiber that shifts the plurality of modulations in refractive index into aperiodic modulations, 
 wherein the plurality of modulations in refractive index includes a first period, a second period, and a third period, the second period located between the first period and the third period, and 
 wherein the first period and the second period are unequal and the second period and the third period are unequal as the length of the optical fiber changes. 
 
     
     
       2. The current sensor of  claim 1 , wherein the externally excited magnetostrictive material comprises Terfenol-D. 
     
     
       3. The current sensor of  claim 1 , wherein the optical fiber is embedded within the strain distribution converter. 
     
     
       4. The current sensor of  claim 1 , wherein the strain distribution converter comprises epoxy. 
     
     
       5. The current sensor of  claim 1 , wherein the externally excited magnetostrictive material comprises a rod having a first end and a second end with a long axis there between, wherein the optical fiber has a long axis, and wherein the long axis of the rod of magnetostrictive material is parallel to the long axis of the optical fiber. 
     
     
       6. The current sensor of  claim 5 , wherein the strain distribution converter comprises a tapered portion having a narrow end opposite a wide end, and wherein the first end of the rod of magnetostrictive material abuts the narrow end of the tapered portion of the strain distribution converter. 
     
     
       7. The current sensor of  claim 6 , wherein the wide end of the strain distribution converter and the second end of the magnetostrictive material are maintained at a fixed distance relative to one another such that changes in size of the magnetostrictive material along the long axis cause changes in a length of the strain distribution converter between the narrow end and the wide end. 
     
     
       8. The current sensor of  claim 7 , wherein the length of the strain distribution converter is a first length at a first point in time and a second length at a second point in time, wherein the first length is larger than the second length, wherein the magnetostrictive material has a larger size along the long axis at the second point in time than at the first point in time. 
     
     
       9. The current sensor of  claim 8 , wherein the strain distribution converter has response profile dependent on strain along the long axis of the strain distribution converter such that a change between the first length and the second length modifies strain along the long axis of the strain distribution converter. 
     
     
       10. The current sensor of  claim 9 , wherein the change between the first length and the second length results in a decrease in length of the strain distribution converter that is greater at the narrow end. 
     
     
       11. The current sensor of  claim 10 , further comprising a non-magnetostrictive sleeve surrounding the rod of magnetostrictive material, wherein the non-magnetostrictive sleeve comprises a material having a similar coefficient of thermal expansion as the magnetostrictive material. 
     
     
       12. The current sensor of  claim 7 , wherein the wide end of the strain distribution converter and the second end of the magnetostrictive material are maintained at a fixed distance relative to one another by a pair of supports. 
     
     
       13. The current sensor of  claim 12 , further comprising
 a second tapered strain distribution converter having a narrow end and a wide end, the wide end of the second tapered strain distribution converter attached to one of the pair of supports, and 
 a second rod comprising a non-magnetostrictive material having a similar coefficient of thermal expansion as the magnetostrictive material, the second rod having a first end and a second end, the first end of the second rod attached to the narrow end of the second tapered strain distribution converter and the second end of the second rod attached to the other of the pair of supports. 
 
     
     
       14. The current sensor of  claim 1 , wherein the externally excited magnetostrictive material is embedded within the strain distribution converter. 
     
     
       15. The current sensor of  claim 14 , wherein the strain distribution converter comprises
 a first end opposite a second end, and 
 a gradation of magnetostrictive material between the first end and the second end. 
 
     
     
       16. The current sensor of  claim 15 , wherein the gradation of magnetostrictive material comprises a continuous gradient. 
     
     
       17. The current sensor of  claim 15 , wherein the gradation of magnetostrictive material comprises a stepwise gradient. 
     
     
       18. The current sensor of  claim 15 , wherein the gradation of magnetostrictive material comprises a gradation of particle sizes ranging in size from about 20 micrometers to about 300 micrometers. 
     
     
       19. The current sensor of  claim 15 , wherein the gradation of magnetostrictive material comprises a range of volume fractions. 
     
     
       20. The current sensor of  claim 15 , wherein the first end of the strain distribution converter comprises a greater amount of magnetostrictive material than the second end of the strain distribution converter. 
     
     
       21. The current sensor of  claim 15 , further comprising a magnetic core having an air gap, wherein the strain distribution converter is disposed within the air gap of the magnetic core. 
     
     
       22. The current sensor of  claim 1 , wherein the optical fiber comprises a fiber Bragg grating, wherein the first period reflects optical signals at a first wavelength, the second period reflects optical signals at a second wavelength, and the third period reflects optical signals at a third wavelength,
 wherein the first wavelength, the second wavelength, and the third wavelength are equal when the plurality of modulations in refractive index are periodic modulations in the initial state, and, 
 wherein the first wavelength, the second wavelength, and the third wavelength are different when the magnetostrictive material is under external excitation and the plurality of modulations in refractive index are aperiodic modulations. 
 
     
     
       23. A current sensor device, comprising:
 a strain distribution converter; 
 an optical fiber that is coupled with the strain distribution converter and that has a plurality of modulations in refractive index, the plurality of modulations in refractive index being periodic modulations in an initial state without external excitation; and 
 an externally excitable magnetostrictive material associated with the strain distribution converter such that a change in shape of the magnetostrictive material under external excitation causes a change in shape of the strain distribution converter that shifts the plurality of modulations in refractive index into aperiodic modulations, 
 wherein the plurality of modulations in refractive index includes a first period, a second period, and a third period, the second period located between the first period and the third period, and 
 wherein the first period and the second period are unequal and the second period and the third period are unequal as the length of the optical fiber changes. 
 
     
     
       24. The current sensor of  claim 23 , wherein the strain distribution converter comprises a composite comprising the externally excited magnetostrictive material. 
     
     
       25. The current sensor of  claim 24 , wherein the composite has a speckle pattern. 
     
     
       26. The current sensor of  claim 25 , further comprising a camera for collecting a plurality of images of the speckle pattern. 
     
     
       27. The current sensor of  claim 26 , further comprising an electronic processor coupled to the camera to receive the plurality of images and configured to analyze the plurality of images using a correlation algorithm to identify a change in shape of the strain distribution converter.